Fin FET and method of fabricating same

ABSTRACT

A fin field effect transistor (fin FET) is formed using a bulk silicon substrate and sufficiently guarantees a top channel length formed under a gate, by forming a recess having a predetermined depth in a fin active region and then by forming the gate in an upper part of the recess. A device isolation film is formed to define a non-active region and a fin active region in a predetermined region of the substrate. In a portion of the device isolation film a first recess is formed, and in a portion of the fin active region a second recess having a depth shallower than the first recess is formed. A gate insulation layer is formed within the second recess, and a gate is formed in an upper part of the second recess. A source/drain region is formed in the fin active region of both sides of a gate electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from Korean Patent Application No.2004-7426, filed on 5 Feb. 2004, the content of which is herebyincorporated by reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates to a semiconductor memory device, and moreparticularly, to a fin field effect transistor where a fin type activeregion is formed.

2. Description of the Related Art

Recently continuous requirements for semiconductor memory devices havinglower power consumption, higher efficiency, and improved speed operationcharacteristics have brought about a continuously reduced design rulefor the purposes of integrating more semiconductor memory devices withina semiconductor chip of a limited size. However, as semiconductor memorydevices become increasingly integrated, the channel length of individualdevices is gradually reduced. This causes a short channel effect,increases the channel doping density of transistors constituting amemory cell, and also increases the junction leakage current.

To solve these problems, fin field effect transistors (fin FETs) thathave a fin-type active region are formed on an SOI (Silicon OnInsulator) silicon substrate and then a gate electrode is formed on thefin region. An example of such a device is disclosed in U.S. Pat. No.6,525,403 entitled “Semiconductor device having MIS field effecttransistors or three-dimensional structure”.

Such a fin FET can effectively control a leakage current generated in achannel and can ensure a channel length, preventing or substantiallyreducing a short channel effect and improving swing characteristics ofthe transistor and decreasing a leakage current. However, there arestill some disadvantages that exist when the fin FET is formed on theSOI silicon substrate because the price of SOI wafers is higher thanbulk wafers and the parasitic source/drain resistance increases.Furthermore, a channel formation body of the semiconductor device is notconnected to the SOI substrate according to a characteristic of the SOIdevice, thus a floating body effect is present, and heat generated inthe device that is typically conducted to the SOI silicon substrate iscut off by an oxide layer formed on the SOI silicon substrate, thusdegrading the performance of the semiconductor device.

Embodiments of the invention address these and other disadvantages ofthe conventional art.

SUMMARY OF THE INVENTION

Exemplary embodiments of the invention provide a method of forming a finfield effect transistor (fin FET) by using a bulk silicon substrate, anda structure thereof. The fin FET is formed by forming a recess having apredetermined depth in a fin active region through use of the bulksilicon substrate, and then by forming a gate on an upper part of therecess, thereby guaranteeing a length of top channel formed under thegate. Also, lengths of top channel and bottom channel are uniformlyformed in the fin active region by increasing a length of the topchannel, thus improving swing characteristics of the fin FET. The topchannel is formed lower than a source/drain region, thus improving adrain induced barrier lowering (DIBL) and reducing an electric field ofchannel and source/drain. The increase of top channel length can alsoreduce an impurity ion implantation amount of a threshold voltagecontrol region formed under a gate, reducing a junction leakage currentof the fin FET and improving refresh characteristics. In forming therecess having a predetermined depth in the fin active region there is noneed to use a specific etch stop layer, thus simplifying a fabricationprocess of the fin FET. An upper edge portion of the fin active regionis rounded, thereby preventing an electric field concentration onto anedge portion and a punch-through in the channel, and uniformly forming agate insulation layer on an upper part of the fin active region.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of exemplary embodiments of the inventionwill become readily apparent from the description that follows, withreference to the attached drawings.

FIG. 1 is a layout diagram of a fin FET according to some embodiments ofthe invention.

FIGS. 2 a to 10 a are sectional diagrams illustrating exemplarysequential processes for forming the fin FET of FIG. 1, taken along theline I-I′ of FIG. 1.

FIGS. 2 b to 10 b, and FIG. 11, are sectional diagrams illustratingexemplary sequential processes for forming the fin FET of FIG. 1, takenalong the line II-II′ of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of the invention are more fully described indetail with reference to the accompanied drawings. The invention may beembodied in many different forms and should not be construed as beinglimited to the exemplary embodiments set forth herein. Rather, theseexemplary embodiments are provided so that this disclosure is thoroughand complete, and to convey the concepts of the invention to thoseskilled in the art.

FIG. 1 is a layout diagram illustrating a fin FET according to someembodiments of the invention.

Referring to FIG. 1, gate electrodes 20 are patterned and disposed inparallel with one another along lines that extend in a first direction,for example, the line II-II′. Fin active regions 10 are disposed alongparallel lines that extend in a second direction, for example, the lineI-I′. The second direction is substantially perpendicular to the firstdirection. The fin active regions 10 are not continuous along theparallel lines that extend in the second direction, but rather the finactive regions 10 are surrounded by a non-active region 30. The finactive regions 10 protrude in a fin shape with step coverage with thenon-active region 30.

With respect to one another, the fin active regions 10 are disposed in adiagonal configuration. That is, a line passing through the centers of afin active region 10 and its closest neighboring fin active region 10 isneither parallel nor perpendicular to the first direction and the seconddirection, but rather has some angular offset with respect to the firstand second directions. Adjacent fin active regions 10 are disposeduniformly, that is, a fin active region 10 and its nearest adjacentneighbors are separated by the same distance. The gate electrodes 20 aredisposed substantially perpendicular to a length direction of the finactive region 10. Two gate electrodes 20 cross over every fin activeregion 10.

FIGS. 2 a to 10 a are sectional diagrams illustrating exemplarysequential processes for forming the fin FET of FIG. 1, taken along theline I-I′ of FIG. 1.

FIGS. 2 b to 10 b and FIG. 11 are sectional diagrams illustratingexemplary sequential processes for forming the fin FET of FIG. 1, takenalong the line II-II′ of FIG. 1.

Referring first to FIGS. 2 a and 2 b, a device isolation film 106 fordefining a non-active region and a fin active region is formed in ap-type bulk silicon substrate 100. The device isolation film 106 isobtained by a device isolation method (e.g., a Shallow Trench Isolation,or STI) where a trench having a predetermined depth is formed in thenon-active region of the substrate, a first oxide layer 102 and anitride layer 104 are sequentially accumulated on a bottom and asidewall of the trench, and then an insulation layer is deposited in thetrench to form the device isolation film 106. Subsequently, a secondoxide layer 107 having a thickness of about 60 Å to 80 Å is formed onthe substrate 100. The device isolation film 106 may be formed to adepth of about 2500 Å to 3000 Å, and may be formed of any one oxidelayer chosen from the group consisting of SOG (Spin-On Glass), USG(Undoped Silicate Glass), BPSG (Boro-Phospo-Silicate Glass), PSG(Phospho-Silicate Glass), PE-TEOS (Plasma Enhanced—TetraEthylOrthoSilicate), and liquid oxide layer material. Alternatively, thedevice isolation film 106 may be formed of a multi-layer involving twoor more of the oxide layer group defined above.

Referring to FIGS. 3 a and 3 b, an anti-reflective coating (ARC) layer108 and a photoresist layer are sequentially formed, and then aphotoresist pattern 110 is formed to expose a gate formation partthrough a photolithography process. The ARC layer 108 may be generallyformed to enhance a resolution of the photolithography process, beforedepositing the photoresist layer.

With reference to FIGS. 4 a and 4 b, the ARC layer 108, the second oxidelayer 107, the device isolation film 106, and the substrate 100 aresequentially etched by using the photoresist pattern 110 as an etchmask, thus forming a first recess 130 having a predetermined depth froman upper surface of the substrate to a portion of the device isolationfilm 106, and also forming a second recess 140 having a depth from theupper surface of the substrate to a portion of the fin active regionthat is shallower than the first recess. The first recess 130 may beformed to a depth of about 1000 Å to 1500 Å, considering a height of thefin active region. The second recess 140 may be formed to a depth ofabout 300 Å to 350 Å to ensure a sufficient length of a top channel thatis formed under a gate electrode, and may be formed by a dual recesstype having two recesses in the active region surrounded by thenon-active region. Also, since only the ARC layer 108 and the secondoxide layer 107 are formed on the substrate, an upper edge portion 109of the fin active region is rounded when etching of the oxide layer 107and the substrate 100 occurs. The rounded upper edge portion 109prevents an electric field concentration on the edge portion, preventschannel punch-through, and uniformly forms a gate insulation layer onthe fin active region.

With reference to FIGS. 5 a and 5 b, p-type impurities are ion implantedby using the photoresist and an anti-reflective coating layer pattern asan ion implantation mask, to thus form a threshold voltage controlregion. For example, B or BF₂ ions may be implanted in the fin activeregion with an energy of about 30 KeV to 50 KeV and having a density ofabout 1.0×10¹² to 1.0×10¹³ ion atoms/cm², thus resulting in a formationof the threshold voltage control region having a density of about1.0×10¹³ ion atoms/cm³. The threshold voltage control region is formedin a lower part of the second recess, which guarantees a sufficientlength for the top channel. Thus, the amount of ion impurities to beimplanted may be reduced.

Referring to FIGS. 6 a and 6 b, the photoresist pattern 110 and the ARClayer 108 are removed by, e.g., an ashing or strip process. This leavesa portion of the nitride layer 104 a and a portion of the first oxidelayer 102 a exposed on a sidewall of the fin active region, as shown inFIG. 6 b.

With reference to FIGS. 7 a and 7 b, the portion of the nitride layer104 a that is exposed on a sidewall of the fin active region is removed,then the portion of the first oxide layer 102 a that is exposed on thesidewall of the fin active region is removed along with the second oxidelayer 107. The nitride layer 104 a may be removed by a wet etching usingH₃PO₄, and the first and second oxide layers 102 a and 107 may beremoved by a wet etching using HF. As a result, as shown in FIG. 7 b, afin active region 111 has step coverage and protrudes with apredetermined height from the surrounding device isolation film 106.

In FIGS. 8 a and 8 b, a gate insulation layer 112 is formed within thesecond recess 140. The gate insulation layer 112 is formed of oxidelayer material, and may be formed by thermally oxidizing a bottom faceof the recess 140 or by a deposition method such as a chemical vapordeposition (CVD) or a sputtering etc.

Referring to FIGS. 9 a and 9 b, a first gate conductive layer 114, asecond gate conductive layer 116, and a capping layer 118, each of whichhave a predetermined thickness, are sequentially formed on thesubstrate. The first gate conductive layer 114 may be formed by ageneral deposition method such as CVD, low pressure chemical vapordeposition (LPCVD), or plasma enhanced chemical vapor deposition(PECVD), and may be formed of polysilicon material. The second gateconductive layer 116 may be formed by a general deposition method, or itmay be formed of a metal such as tungsten (W) or of a silicide layerhaving a metal such as Ti, Ta, W, Ni, Cr, Ir or Ru. The first and secondconductive layers 114 and 116 constitute a gate electrode, and may beformed of a single layer of polysilicon material. The capping layer 118may be formed of silicon nitride layer material through a process suchas, e.g., CVD, LPCVD, PECVD, a semi-atmospheric chemical vapordeposition (SACVD), a sputtering method, or an atomic layer deposition.

As shown in FIGS. 10 a and 10 b, a photolithography and etching processis performed, to thus form a gate stack 119 that has a gate conductivelayer 114 that extends to an upper surface of the fin active region 111and has a capping layer 118 on the gate conductive layer, within thesecond recess.

Referring to FIG. 11, after forming a gate spacer 122 in a sidewall ofthe gate stack 119, n-type impurities such as P (phosphorous) or As(Arsenic), etc., is ion implanted at an energy of about 10 KeV to 20 KeVand to a density of about 1.0×10¹⁵ to 3.0×10¹⁵ ion atoms/cm², by usingthe gate spacer 122 as an ion implantation mask, to thus form an n+ typesource/drain region 120 of a high density in the fin active region ofboth sides of the gate electrode. Also, before forming the gate spacer122, n type impurities are ion-implanted at a relatively low energy andto a relatively low density compared to the source/drain regions 120,thus forming a low density n-type source/drain region. Next, a n+ typesource/drain region having a density higher than the low density n-typesource/drain region is formed on a portion of the low density n-typesource/drain region. Thus, a source/drain region having a LDD (LightlyDoped Drain) structure is obtained.

Accordingly, according to an exemplary embodiments of the invention, themethod of forming a fin FET provides a fin field effect transistor (finFET), including the device isolation film 106 defining a fin activeregion and a non-active region on a bulk silicon substrate; the finactive region 111 having a protrusion shape with step coverage of apredetermined height with the device isolation film; the gate electrodes114 and 116, which have a predetermined depth from a surface of the finactive region and is extended to an upper surface of the fin activeregion; the gate insulation layer 112 formed under the gate electrode;and the source/drain region formed in the fin active region of bothsides of the gate electrode. An uppermost part of the fin active regionis formed higher by about 1000 Å to 1500 Å than an uppermost part of thedevice isolation film. An upper edge portion of the fin active region isrounding processed. The gate electrode has a depth of about 300 Å to 350Å from an upper surface of the fin active region, and a bottom face ofthe gate electrode is rounding processed. The gate electrode has a dualgate structure.

In such a method of forming the fin FET and in such a structure thereofaccording to an exemplary embodiment of the invention, the fin FET isformed by using a bulk silicon substrate, that is, a recess having apredetermined depth is formed in a fin active region, and then a gate isformed in an upper part of the recess such that a length of top channelformed under the gate is sufficiently guaranteed. Also, lengths of topchannel and bottom channel are uniformly formed in the fin active regionby increasing a length of the top channel, thus improving swingcharacteristics of the fin FET. The top channel is formed lower than asource/drain region, thus improving a drain induced barrier lowering(DIBL) and reducing an electric field of channel and source/draintogether with enhancing characteristics of the fin FET.

The length increase of top channel can also reduce an impurity ionimplantation amount of a threshold voltage control region formed under agate, thus reducing a junction leakage current of the fin FET andimproving refresh characteristics.

Also, when forming the recess having a predetermined depth in the finactive region, a specific etch stop layer is unnecessary, thussimplifying a fabrication process of the fin FET. An upper edge portionof the fin active region is rounding processed, whereby preventing anelectric field concentration onto an edge portion and a punch-through ofchannel, and uniformly forming a gate insulation layer on the fin activeregion.

As described above, in forming a fin FET by using a bulk siliconsubstrate, a recess having a predetermined depth is formed in a finactive region and then a gate is formed in an upper part of the recess,thereby sufficiently guaranteeing a length of top channel formed underthe gate.

In addition, a length of top channel increases, thereby uniformlyforming lengths of top and bottom channels in the fin active region, andimproving swing characteristics of the fin FET. The top channel isformed at a position lower than a source/drain region, thus improving adrain induced barrier lowering (DIBL) and reducing an electric field ofchannel and source/drain, with enhancing characteristics of the fin FET.

A junction leakage current of the fin FET is reduced and a refreshcharacteristic is enhanced by increasing a top channel length and so byreducing an impurity ion implantation amount of a threshold voltagecontrol region formed under a gate.

In forming a recess having a predetermined depth in a fin active region,a specific etch stop layer is unnecessary, thus simplifying afabrication process of fin FET. Also, an upper edge portion of the finactive region is rounding processed, whereby preventing an electricfield concentration onto an edge portion and a punch-through of channel,and uniformly forming a gate insulation layer on an upper part of thefin active region.

Embodiments of the invention may be practiced in many ways. What followsare exemplary, non-limiting descriptions of some of these embodiments.

An embodiment of the invention provides a method of forming a fin FET byusing a bulk silicon substrate. The method includes forming a deviceisolation film for defining a non-active region and a fin active regionin a predetermined region of the substrate; forming a first recesshaving a predetermined depth from an upper surface of the substrate on aportion of the device isolation film, and a second recess having a depthshallower than the first recess on a portion of the fin active region;forming a gate insulation layer within the second recess; forming a gatein an upper part of the second recess; and forming a source/drain regionin the fin active region of both sides of the gate.

Other embodiments of the invention provides a structure of fin fieldeffect transistor (fin FET) formed on a bulk silicon substrate on whichan active region and a non-active region are defined by a deviceisolation film. The structure includes a fin active region having aprotrusion shape with step coverage of a predetermined height with thedevice isolation film, in the device isolation film; a gate electrode,which has a predetermined depth from a surface of the fin active regionand is extended to an upper surface of the fin active region; a gateinsulation layer formed under the gate electrode; and a source/drainregion formed in the fin active region of both sides of the gateelectrode.

It will be apparent to those skilled in the art that modifications andvariations can be made in the present invention without deviating fromthe spirit or scope of the invention. For example, a fin FET may beformed by using a substrate and impurities of contrary conductive typeand may be provided as a plurality of fin FETs connected to a capacitor,to constitute a memory cell. Thus, it is intended that the presentinvention cover any such modifications and variations of this inventionprovided they come within the scope of the appended claims and theirequivalents

1. A method of forming a fin field effect transistor (fin FET) by usinga bulk silicon substrate, said method comprising: defining a non-activeregion and a fin active region on a predetermined region of the bulksilicon substrate with a device isolation film; etching a portion of thedevice isolation film to form a first recess having a first depthmeasured from an upper surface of the fin active region and etching aportion of the fin active region to form a second recess having a seconddepth measured from the upper surface of the fin active region, thesecond depth less than the first depth; depositing a gate insulationlayer within the second recess; forming a gate in an upper part of thesecond recess; and forming a source/drain region in the fin activeregion on both sides of the gate.
 2. The method of claim 1, whereinetching the portion of the device isolation film to form the firstrecess having the first depth comprises etching the device isolationfilm so that the first depth is about 1000 Å to 1500 Å.
 3. The method ofclaim 1, wherein etching the portion of the fin active region to formthe second recess having the second depth comprises etching the finactive region so that the second depth is about 300 Å to 350 Å.
 4. Themethod of claim 1, further comprising etching another portion of the finactive region to form a third recess having a third depth measured fromthe upper surface of the fin active region, the third depthsubstantially equal to the second depth.
 5. The method of claim 1,wherein etching the portion of the device isolation film and etching theportion of the fin active region comprises: depositing an oxide layer onthe substrate after forming the device isolation film; depositing ananti-reflective coating layer and a photoresist layer on the oxidelayer; photolithographically processing the photoresist layer to form aphotoresist pattern for exposing a gate formation part; etching theportion of the device isolation film and etching the portion of the finactive region using the photoresist pattern as an etch mask; andremoving the photoresist pattern and the anti-reflective coating layer.6. The method of claim 1, further comprising, after forming the firstand second recesses, ion-implanting impurities in a lower part of thesecond recess to form a threshold voltage control region.
 7. The methodof claim 1, wherein defining the non-active region and the fin activeregion comprises: opening a trench having a predetermined depth in thenon-active region of the substrate; accumulating an oxide layer and anitride layer on a sidewall of the trench; and filling the trench withan insulation layer to form the device isolation film.
 8. The method ofclaim 7, wherein opening the trench comprises opening the trench to adepth of about 2500 Å to 3000 Å.
 9. The method of claim 7, whereinfilling the trench with the insulation layer comprises filling thetrench with at least one oxide layer selected from the group consistingof SOG, USG, BPSG, PSG, PE-TEOS and liquid oxide layer material.
 10. Themethod of claim 1, wherein depositing the gate insulation layercomprises depositing an oxide layer material.
 11. The method of claim 1,wherein forming the gate comprises: filling the first and secondrecesses with a conductive material to form a gate conductive layer thatextends above the upper surface of the fin active region; depositing acapping layer on the gate conductive layer; etching the capping layerand the gate conductive layer to form a gate stack that extends abovethe second recess; and depositing a gate spacer on a sidewall of thegate stack.
 12. The method of claim 11, wherein forming the gate furthercomprises forming the gate of a single polysilicon layer or of amulti-layer polycide structure.
 13. The method of claim 11, whereindepositing the capping layer comprises depositing a silicon nitridematerial.
 14. The method of claim 1, wherein forming the source/drainregion comprises forming a lightly doped drain (LDD) structure having alow-density source/drain region and a high-density source/drain region.15. A structure of a fin field effect transistor (fin FET) formed on abulk silicon substrate on which an active region and a non-active regionare defined by a device isolation film, said structure comprising: a finactive region having a protrusion shape with a step coverage ofpredetermined height from the device isolation film; a gate electrodethat has a predetermined depth from an upper surface of the fin activeregion and extends beyond the upper surface of the fin active region; agate insulation layer disposed between the fin active region and thegate electrode; and a source/drain region disposed in the fin activeregion on both sides of the gate electrode.
 16. The structure of claim15, wherein the upper surface of the fin active region is about 1000 Åto 1500 Å taller than an upper surface of the device isolation film. 17.The structure of claim 15, wherein an upper edge portion of the finactive region is rounded.
 18. The structure of claim 15, wherein thegate electrode has a depth of about 300 Å to 350 Å from the uppersurface of the fin active region.
 19. The structure of claim 15, whereina bottom face of the gate electrode is rounded and has a predetermineddepth from the upper surface of the fin active region.
 20. The structureof claim 15, further comprising a threshold voltage control regiondisposed beneath the gate insulation layer.
 21. The structure of claim15, wherein the gate electrode has a dual gate structure.